The issue has come to light following the publication of a research paper by University of California, Los Angeles professor Chunyi Peng, who found telcos generally count data usage correctly, but customers who use their device in areas with weak signal strength or to stream audio or video are often overcharged.

Vodafone confirmed the issue affected them. Optus said it had not seen examples of the issue but that in some instances data usage may be affected by a customer's data session being interrupted, while Telstra advised that it had protocols in place to protect overcharging but wouldn't guarantee they worked 100 per cent of the time.

The problem arises due to the way most networks count data usage, according to the professor's research. Under most current charging systems, the data is charged as it is sent from the telco's network to the customer, but the telco generally does not confirm if the data has actually been received.

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"The root causes lie in lack of both co-ordination between the charging system and the end device, and prudent policy enforcement by certain operators," Peng wrote in her research paper, which was put together with the help of three other researchers and looked at how data was charged on two US mobile networks.

Overall, the research showed that the average overcharge was about five to seven per cent for most users.

Peng's solution? A system that confirms receipt of mobile data packets.

"We believe that the network has to take [a] more central role in the charging process, while the end devices offer useful hints and feedback to the network," she said.

Customers who use networks that suffer from congestion or poor coverage may notice the problem arise more regularly when checking their bills with a keen eye, such as one Vodafone customer who contacted Fairfax Media but did not wish to be named. Customers with a phone or mobile broadband dongle on plans that includes unlimited data — which is rare in Australia but available on some networks — would not notice the issue being much of a problem at all.

Optus and Vodafone conceded that their systems were not fool-proof and could overcharge customers for data.

A spokesman for Telstra would only say that the company had "a range of protocols in place to help prevent customers being charged for data they do not receive". Pushed to answer whether those protocols always worked, the spokesman said Telstra had "confidence" in them and did "everything possible to prevent overcharging occurring".

"If a customer has a concern, we would encourage them to let us know," the spokesman said.

Optus said it recognised "in some instances" data usage may be counted to a customer's plan even if the session had been interrupted and the data not received.

"Optus has a process in place whereby customers who have a query with their data charges can report them for investigation," it said. "In these instances, we take the necessary steps to investigate any discrepancies, and ensure that these are resolved for our customers."

A spokeswoman for Vodafone said it was possible that a customer's attempt to transmit or receive data may not be successful, but this would consume "minimal data" and only constitute as a "potential micro charge" on a customer's mobile phone bill.

"This being the case, such transactions can not accumulate to result in any form of bill shock," she said.

Vodafone's spokeswoman said poor connection to its network with a mobile phone or broadband dongle or a lack of response from a website were just some of the reasons a customer could be charged for data their mobile device never received.

"This is common to all mobile networks and fixed-line Internet Service Providers," she said.

Randal Markey, a spokesman for the Australian Mobile Telecommunications Association, which represents Australian mobile telcos, said it was possible for a customer to be charged for data they haven't used because of a "technical inability" to distinguish if data sent has been received by the customer. "This could occur if the connection dropped out, however, it should be noted that most customers have data plans with generous allowances that would more than offset such an occurrence and ensure that they did not breach their data limits."

Markey added that interruptions to service where data is lost would account for "a very small proportion" of customers' plans, and unless a customer exceed their data caps, they wouldn't be charged more. "If consumers feel they may have been overcharged they should always contact their service provider in the first instance."

Elise Davidson, a spokeswoman for the Australian Communications Consumer Action Network, the peak body that represents consumers on communications issues, said there was a likelihood that customers in areas with poor coverage would appear to have used more data than they had actually received.

"These small amounts of data will count against the customer's monthly allowance, but there's no way of calculating the cost of that by looking at a phone bill."

She said this highlighted one of the main problems consumers experience around data charges — consumers only know how much data actually "costs" when they go over their limit.

"Within a post-paid plan, there is no transparency around pricing for data and in terms of actual usage, it is almost impossible for a consumer to argue against what a provider has recorded," she said. "This is why complaints to the Telecommunications Industry Ombudsman last year about disputed internet charges were up 150 per cent — 83 per cent of them relate to smartphones."

Comments made by Optus in this article have been clarified since publication